A 58-year-old male factory worker presents with progressive bilateral hearing loss over 15 years. He reports difficulty hearing high-pitched sounds and tinnitus. Otoscopy is normal. Pure tone audiometry shows bone conduction thresholds within normal limits (0–15 dB HL), while air conduction thresholds are elevated at 500 Hz (35 dB HL), 1000 Hz (40 dB HL), 2000 Hz (50 dB HL), 4000 Hz (65 dB HL), and 8000 Hz (60 dB HL). Speech discrimination is 70%. What is the most likely diagnosis?